This invention is concerned with improvements in shredding machines.
A conventional shredding machine (hereinafter referred to as being of the kind specified) comprises a housing in which a shredding mechanism is mounted, drive means being provided for the shredding mechanism. Mounted over the housing is a cover provided with a slot through which material to be shredded is fed, into engagement with shredding mechanism of the machine.
Desirably sensing means is provided in the machine, to terminate operation of the drive means when the machine is not being used, or when use has been completed. A convenient sensing means which may conveniently be incorporated into the machine comprises an optical sensor, responsive to the presence of a sheet of paper in the slot to activate, or permit activation of the drive means, and to terminate operation of the drive means when the paper has passed through the slot.
Such sensing means are expensive, and an alternative sensing means may be provided by a microswitch having an operating member which is spring-urged into an operative position in which it extends across the mouth. The operating member is thus engaged by the paper as it is inserted into the slot, to cause the microswitch to close and to cause operation of the shredding mechanism to commerce.
However, a further problem with shredding machines of the kind specified is that, to allow complete passage of material through the slot and through the shredding mechanism, it is necessary to utilise a time delay to maintain operation of the shredding mechanism for a short period of time subsequent to completion of passage of the material beyond the operating member. Conventionally such a time delay is afforded by an electronic mechanism, which adds to the cost of the machine.
According to this invention there is provided a shredding machine comprising:
a) a housing;
b) shredding mechanism in the housing;
c) a slot in the housing, through which material to be shredded enters the housing; and
d) and operating member urged by resilient means into an operative position in which it extends across the mouth of the slot, to be moved to an inoperative position by entry of the material to be shredded into the housing, to cause the shredding mechanism to operate;
characterised in that there is interposed between the resilient means and the operating member a motion damping device.
Conveniently, the resilient means is provided by spring means by which the plunger of a microswitch is urged to its open condition. Thus movement of the operating member to its inoperative position causes movement of the damping device against the plunger of the microswitch, causing the microswitch to adopt its closed condition, to cause the shredding mechanism to operate. On passage of the material beyond the mouth, the operating member is released, and the damping device retards movement of the resilient means, delaying switching of the microswitch for a short period of time sufficient to allow completion of passage of material into the shredding mechanism.
According to this invention there is also provided a shredding machine comprising
a) a housing;
b) shredding mechanism in the housing;
c) a drive motor in the housing to drive the shredding mechanism;
d) control means in the housing for the drive motor, said control means comprising a microswitch having a plunger spring-urged into a circuit-open condition;
e) a slot in the housing through which material to be shredded may enter the housing; and
f) an operating member mounted adjacent the slot for movement between an operative position in which it extends across the mouth of the slot, and an inoperative position, movement of the operating member to its inoperative position being caused by entry of material to be shredded into the slot, the microswitch providing resilient means whereby the operating member is urged into its operative position,
characterised in that there is interposed between the operating member and the resilient means a motion damping device whereby movement of the operating member under the action of the resilient means to its operative position is retarded.
Conveniently the damping device is a rotary damping device comprising a shallow cylindrical housing, and a drive member mounted in the housing with a small clearance between the interior wall of the housing and the exterior wall of the drive member, there being a viscous material, such as a viscous oil or elastomeric material, in said space to retard rotary movement of the drive member within the housing. Preferably attached to the drive member is a drive arm, extending generally diametrically of the device, one end of which engages the operating member, the other end of which engages the plunger of the microswitch.
Preferably said operating arm is L-shaped, and conveniently the operating member is freely mounted for movement relative to the housing of the machine.
According to this invention there is also provided a method of providing a time delay in a shredding machine to maintain operation of the shredding mechanism for a short period of time subsequent to completion of passage of the material through an entry slot of the machine, in which the delay is afforded by the use of a motion damping device.